Apparatus for recording and reproducing digital signals on magnetic tape

Abstract

An apparatus for recording and reproducing a digital data signal carrying digital information at each periodically appearing reference "P1" phase includes a detector for detecting and producing a phase data signal at each sampling point. Two subsequently sampled phase data are stored in latches for use of the digital data signal by three signal comparators. The first comparator compares the first sampled phase data signal and the second sampled phase data signal. The second comparator compares the first sampled phase data signal with a predetermined value, and the third comparator compares the second sampled phase data signal with the same predetermined value. Utilizing the outputs of the three comparators, a phase condition detector detects whether or not a reference phase is contained between two subsequent sampling points. A detection pulse generator is provided which generates a data detection pulse when the phase condition detector detects the reference phase.

What is claimed is: 
     
       1. An apparatus for recording and reproducing a digital data signal carrying digital information, comprising: detecting means for detecting and producing a phase data signal at a sampled point of said digital data signal;   first storing means for storing a first phase data signal at a first sampling point;   second storing means for storing a second phase data signal at a second sampling point which is immediately before said first sampling point;   first comparator means for comparing said first phase data signal and said second phase data signal;   second comparator means for comparing said first phase data signal with a first predetermined value;   third comparator means for comparing said second phase data signal with a second predetermined value;   phase condition detecting means responsive to the outputs of said first, second and third comparators for detecting whether or not a reference phase is contained between said first and second sampling points; and   data detection pulse generating means for generating a data detection pulse when said phase condition detecting means detects said reference phase between said first and second sampling points.   
     
     
       2. An apparatus as claimed in claim 1 and further comprising zero-crossing detecting means for detecting a zero-crossing during a sampling period between said first and second sampling points, and wherein said data detection pulse generating means generates said data detection pulse when said zero-crossing detecting means detects a zero-crossing in both of two subsequent sampling periods. 
     
     
       3. An apparatus as claimed in claim 2, and further comprising: means for producing a phase difference representing a difference between a zero-crossing point and the next sampling point;   third storing means for storing said phase difference;   subtract or means for obtaining a phase difference between said first phase data and a third predetermined value;   fourth comparing means for comparing the output of said subtract r with the output of said phase difference producing means; and   data detecting means for detecting a digital information carried in said data signal based on the output of said fourth comparing means.   
     
     
       4. An apparatus as claimed in claim 3 and wherein said first, second and third predetermined value comprises equal values. 
     
     
       5. An apparatus as claimed in claim 1, further comprising means for detecting the sign of zero data such that the zero data is detected as having a sign of plus (+) when said zero data is detected during the decrease of said data signal, and as having a sign of minus (-) when said zero data is detected during the increase thereof. 
     
     
       6. An apparatus as claimed in claim 1 and wherein said first and second predetermined value comprises equal values.